In an electronic device 10, an integrated circuit 12 is attached to a substrate 14, which may be made of glass, as illustrated in FIG. 1. The integrated circuit 12 includes aluminum pads 16, gold bumps 18, and a passivation layer 20. The substrate 14 includes patterns 22, which are electrically connected to the gold bumps 18 of the integrated circuit 12 via conductive particles 24 contained in an adhesive 26. The conductive particles 24 may be made of gold, silver, nickel, metal coated glass, metal coated silica, or a metal coated polymer. The conductive particles 24 in the adhesive 26 are trapped between the patterns 22 on the substrate 14 and the gold bumps 18 on the integrated circuit 12 to make electrical connections 28 therebetween. However, the conductive particles 24 may also form a short circuit 30 between a first electrical connection 32 and a second electrical connection 34, thereby causing a short circuit in the electronic device 10.
One approach to solving this short circuiting problem is illustrated in FIG. 2. In this approach, the conductive particles 24 are selectively deposited onto the gold bumps 18 on the integrated circuit 12, before attaching the integrated circuit 12 to the substrate 14. The integrated circuit 12 and the substrate 14 are then attached with a non-conductive paste 36. This method is extremely expensive and time consuming, since it is very difficult to place the conductive particles 24 on the gold bumps 18. Further, integrated circuits are not typically sold with conductive particles on the aluminum pads. As a result, this technique is not suitable for mass producing an electronic device, which includes numerous integrated circuits, attached to a substrate.
A second solution to the short circuit problem identified above is illustrated in FIG. 3. In this method, the substrate 14 and patterns 22 residing thereon are coated with a positive acting photoimagable photoresist 38, mixed with conductive particles 24, as illustrated in FIG. 3(a). Ultraviolet light is applied to a backside of the substrate 12 and a portion of the positive acting photoimagable photoresist 38 which is exposed (namely the portions between the patterns 22) washes away, leaving the conductive particles 24 on top of the patterns 22 of the substrate 14, as illustrated in FIG. 3(b). The substrate 14 is then attached to the integrated circuit 12 using a nonconductive adhesive 36. This technique is also time consuming and expensive, since the positive acting photoimagable photoresist 38 must be carefully applied to the patterns 22 of the substrate 12, in order to ensure that a uniform layer of conducting particles 24 are applied on top of the patterns 22 of the substrate 12. Further, this technique is impractical for large area substrates and is not easily integrated into existing manufacturing processes.
A third technique for solving the short-circuiting problem includes the addition of a dielectric barrier 40, between two patterns 12 on the substrate 14, as illustrated in FIG. 4. However, in this arrangement, the dielectric barrier 40 is likely to force the conductive particles 24, as illustrated in FIG. 4, to form a short-circuit 30 between first 42 and second 44 electrical connections.
The invention described in this specification solves the problem of short circuiting between electrical connections when using a adhesive, by providing a peak-shaped dielectric dam between the two electrical connections, in order to minimize the possibility that the conductive particles of the adhesive will form a short circuit between the two electrical connections. The present specification also discloses a novel method for manufacturing the peak-shaped dielectric dam, which is fast and inexpensive, and therefore suitable for the mass production of electronic devices, which include numerous interconnections between integrated circuits and substrates.